1. Technical Field
The present invention relates to a resonator element, a resonator, a resonator device, an oscillator, an electronic apparatus, and a moving object.
2. Related Art
In the related art, there are known resonator elements using quartz crystal. Such resonator elements are widely used as reference frequency sources, oscillation sources, or the like of various electronic apparatuses since frequency-temperature characteristics are excellent. In particular, since the frequency-temperature characteristics of resonator elements using quartz crystal substrates cut at cut angles called AT-cut show cubic curves, the resonator elements are widely used in mobile communication apparatuses such as mobile phones.
For example, JP-A-2012-114496 and JP-A-2012-114495 disclose AT-cut quartz crystal resonator elements which have multistage mesa structures and in which vibration sections which are mesa sections include first portions and second portions having thicknesses thinner than the first portions and integrated in the circumferences of the first portions in a plan view. Here, when Z is the size of an AT-cut substrate in a Z′ axis, Mz is the size of the vibration section in the Z′ axis, and t is the thickness of the first portion of the vibration section and relations of “8≦Z/t≦11” and “0.6≦Mz/Z≦0.8” are satisfied, it is possible to reduce the value of equivalent series resistance, so-called crystal impedance (CI).
JP-A-2012-191300 and JP-A-2012-191299 disclose AT-cut quartz crystal resonator elements having multistage mesa structures. Here, by forming protrusions on free end sides, a package and an excitation electrode formed in the vibration section are prevented from coming into contact with each other at the time of mounting on the package.
JP-A-2011-97183 discloses an AT-cut quartz crystal resonator element having a multistage mesa structure. Here, by forming protrusions so that a vibration section is interposed between the protrusions, flexural vibration is prevented.
In the foregoing resonator elements, however, when protrusions are formed at positions at which vibration displacement energy in the vibration sections is not sufficiently attenuated, vibrations of excitation portions are affected, and thus electric characteristics of the resonator elements may deteriorate in some cases.